The long-range efforts of this laboratory are directed towards understanding the molecular mechanisms involved in the repair of ionizing radiation damage. To do this we are using a variety of approaches utilizing organisms amenable to both genetic and biochemical techniques. To examine presumptive excision repair of base damage, we have and shall continue to utilize the genetically well characterized organisms, Escherichia coli and Saccharomyces cerevisiae, to attempt to identify enzymes that recognize x-irradiated DNA substrates and to assign particular genes to the enzymes involved. For post replication repair studies, the recombinational repair-deficient bacteriophage T4 mutants, x, y and w are being examined for their particular deficiencies. Further, we are cloning the y and w genes so that we can amplify their products for purification. Lastly, to quantify ionizing radiation damage to DNA so that we may more accurately study repair processes, we are utilizing PM2 bacteriophage and PM2 transfecting DNA as a model system.